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Right answer is (c) testing insulation RESISTANCE

To explain I WOULD say: A null detector is used to balance the bridge. Additional e.m.f can be provided to a CIRCUIT by INCREASING the MAGNITUDE of the voltage source. Megger is used for testing the insulation resistance of cables.

The correct ANSWER is (b) source to MEASURE high resistance

Easy explanation: MEGGER is a portable instrument to measure high resistances.

The correct ANSWER is (a) 0.1 Mῼ

The explanation: Resistances of the order of 0.1 Mῼ and above are KNOWN as HIGH resistances. Resistance VALUES upto 1 ῼ are known as low resistances. Resistances upto a few kῼ are known as medium resistances.

Right ANSWER is (a) INDUCTANCE and Quality factor value

Best explanation: In its basic form a Kelvin bridge is USED for the measurement of low resistance. A Kelvin bridge can be used for the measurement of inductance and Quality factor value through CALIBRATION.

The correct option is (b) due to balance problem

Easy explanation: A Kelvin bridge can be USED for the measurement of high Quality factor values. Due to bridge IMBALANCE problem, Kelvin bridge can’t be used for MEASURING LOW Quality factor values.

Right answer is (d) high current

The BEST I can EXPLAIN: The condition to ACHIEVE a high SENSITIVITY in a Kelvin bridge is that the measuring current should be high enough so as to sensitize the null detector.

Correct answer is (c) due to contact and lead resistance

Explanation: While measuring very LOW resistances the contact and lead resistances cause SIGNIFICANT errors in the VALUE of the measured resistance. As a result Kelvin bridge is used for measurement of low resistances.

Right choice is (c) ±0.05 to ±0.2 %

EASY EXPLANATION: As Kelvin bridge is used for the measurement of low resistance VALUES, the ACCURACY of measurement of low resistances in a Kelvin bridge is of the order of ±0.05 to ±0.2 %.

Correct choice is (a) independent

Best explanation: Effect of contact and lead RESISTANCES are completely eliminated in a KELVIN BRIDGE as they don’t APPEAR in the balance equation. Hence the Kelvin bridge is independent of the load and contact resistances.

Right answer is (d) Rx = \(\FRAC{R_1 R_3}{R_2}\)

Best explanation: The balance equation in a KELVIN bridge is GIVEN by the relation Rx = \(\frac{R_1 R_3}{R_2}\)

where,

R1, R2, R3, and Rx form the ratio arms

Rx is the value of the unknown resistance.

Correct OPTION is (a) double bridge

Explanation: Kelvin’s bridge consists of two additional ARMS COMPARED to a WHEATSTONE bridge. Hence it is ALSO known as a double bridge.

The CORRECT choice is (a) I = IV + Ir

To explain: By applying Kirchhoff’s current law at the node N from FIG we get,

I = IV + Ir

where,

I is the total series current flowing through the circuit

Iv is the current flowing through the voltmeter

Ir is the current flowing through the resistance R.

The correct answer is (c) KELVIN double bridge method

To elaborate: Kelvin’s double bridge is used for the measurement of low RESISTANCES of the ORDER of 1ῼ or less. Ammeter voltmeter method is used for the measurement of current flowing through and the VOLTAGE across the circuit.

Correct answer is (a) CONTACT resistance drops at the leads

To explain I WOULD say: As the current FLOWING through a LOW resistance CIRCUIT is low, the voltage drop across the terminals due to contact and lead resistances is negligible. Thermal e.m.f occurs in a circuit when its temperature increases due to high current flow.

Correct answer is (d) It does not contain any contact RESISTANCE

Best explanation: The voltage DROP measured ACROSS a LOW resistance does not contain any contact and lead RESISTANCES of the components and is independent of it.

Right answer is (b) contact and lead resistances are appreciable

Easy EXPLANATION: When MEASURING low resistances of the ORDER of 1 ῼ or even less, lead and contact resistances of the order of even 0.002 ῼ cannot be neglected. High CURRENTS FLOW through low resistance circuits.

Correct answer is (b) by KEEPING the LEAD wire resistances within 0.2 mΩ

The best I can explain: The DRIFT in the MEASURED value of resistance in a Wheatstone bridge can be minimized by maintaining the lead wire resistances within 0.2 mΩ. As a result, the EFFECT of lead wire resistance gets removed in the output value of the bridge circuit.

Correct choice is (d) DUE to LEAD wires

To elaborate: Lead wires ADD to the RESISTANCE of the arms of the Wheatstone bridge. As a RESULT the bridge circuit is destabilized and can’t be used for signal conditioning.

Correct option is (c) desensitizes the system

To elaborate: The LEAD wires connecting the resistance arms of a WHEATSTONE bridge add to the existing values of resistances across the ratio arms. As a result the NET value of resistance changes, thus destabilizing the system.

The CORRECT choice is (c) GALVANOMETER becomes insensitive to an imbalance

The BEST I can explain: If the Wheatstone BRIDGE is used for the measurement of high RESISTANCE, the galvanometer becomes insensitive and does not detect any imbalance.

Correct OPTION is (a) high resistance

Explanation: Wheatstone bridge can be used for the MEASUREMENT of medium resistances only. KELVIN bridge is used for the measurement of medium resistances.

The correct answer is (B) high

To elaborate: As the resistance MUST have a tolerance of upto 1%, cost of maintenance of the Wheatstone BRIDGE circuit is expensive. Voltage SOURCE does not add to the cost of maintenance of a Wheatstone bridge as it is uniform for all bridge CIRCUITS.

Right choice is (a) USING more than ONE resistive sensor

To explain I would say: By making USE of more than one resistive sensor within the four ARMS of a Wheatstone bridge we get a full bridge, half bridge or a QUARTER bridge setup with an automatic balancing effect.

The CORRECT answer is (c) light measurement

For EXPLANATION: WHEATSTONE bridge consists of simple resistances in the ratio arms. One of the simplest APPLICATIONS of a Wheatstone bridge is the measurement of light by making use of a photo resistive device.

Right option is (b) ALONG with an OP amp

Explanation: A Wheatstone BRIDGE can be used for the measurement of physical parameters such as TEMPERATURE, strain, light, etc by making use of an operational amplifier. Rectifier circuits are used for the conversion of ac to DC.

Correct ANSWER is (a) line to line or line to ground

Explanation: In a telephone line, line to line and line to ground faults OCCUR. Symmetrical, unsymmetrical, open circuit, short circuit, triple line to line and line to ground faults occur in POWER SYSTEMS.

The CORRECT choice is (d) locating the cable faults

Easy explanation: Cable faults in telephones can be located by telephone companies by MAKING use of a Wheatstone BRIDGE. TELEPHONIC resistances are determined using suitable techniques. Dialtone is maintained through optical fibre technology.

The correct ANSWER is (c) quality CONTROL of wire

Explanation: Wheatstone bridge is used to measure the d.c. RESISTANCE of various types of wires for controlling the quality of the wires. Voltage SOURCE MAINTAINS a constant e.m.f in the bridge circuit.

The correct answer is (a) 1Ω to a few MEGAOHMS

Easy EXPLANATION: Wheatstone bridge is the simplest form of bridge CIRCUIT. It is BASICALLY used for the MEASUREMENT of medium resistances in the range of 1Ω to a few megaohms.

Right choice is (b) d.c. BRIDGE

The explanation: The Wheatstone bridge is a d.c. bridge that is used for the measurement of MEDIUM resistance. Schering bridge is used for measurement of high voltages. AC BRIDGES comprise of Anderson bridge, MAXWELL Bridge, ETC.

The correct answer is (a) using more sensitive galvanometers

The BEST I can explain: Thermal emf can be ELIMINATED by making use of sensitive galvanometers consisting of COPPER coils and copper suspension systems. DISSIMILAR metals can’t be physically separated.

Correct choice is (d) when dissimilar metals come in contact

The best I can EXPLAIN: When dissimilar metals come into contact with each other in a GALVANOMETER circuit, thermal emf is generated. NULL DETECTOR is used for detecting the balance condition.

Right ANSWER is (c) lead and contact RESISTANCE

The explanation is: Voltage drop across the circuit along with power dissipation lead to errors in the measurement of LOW resistances. The resistance of LEADS and contacts of the external circuit adds to the values in the circuit. This is the MAIN source of error while measuring low resistances.

Right option is (b) limiting CURRENT to a safe VALUE

For explanation I WOULD say: Heating EFFECT can be eliminated by limiting the current through the circuit to a safe value and by calculating the power dissipation in the arms. Heat SINKS are typically used in power electronic applications.

The correct option is (a) directly proportional

To EXPLAIN: TEMPERATURE AFFECTS RESISTANCE of the circuit. Resistance has a positive temperature COEFFICIENT and increases linearly with rise in temperature.

The correct option is (d) TEMPERATURE increases due to power dissipation

To EXPLAIN: Current flow through the resistances causes power dissipation i.e. I^2R LEADING to an INCREASE in the temperature. As the BRIDGE consists of pure resistances, there is no back e.m.f induced.

Correct choice is (a) 1ῼ to a few megaohms

Explanation: A Wheatstone BRIDGE is used for the measurement of medium RESISTANCE in the range of 1ῼ to a few megaohms. Kelvin bridge is used for the measurement of low resistance.